The present invention relates in general to a structure and a method for forming a converging-type electron-emission source of a field-emission display, and more particularly, to a method of forming a recessed region or a slot in a cathode structure and a carbon nanotube in the recessed region, such that the peripheral electrode layer protrudes over the electron-emission source. In addition, the protruding electrode layer forms the potential distribution to achieve converging effect of the electron beam.
In the conventional bipolar or tri-polar field-emission display having a carbon nanotube as an electron-emission source (as shown in FIGS. 1 and 2), the electrons are drained from the electron-emission source to impinge the phosphor layer of the anode, so as to excite the phosphor to illuminate. The configuration of the cathode and anode often causes the electron beams diverged due to the electric field. Sometimes the electron beams may even impinge the phosphor of the neighboring anode unit to cause gamut. The image display by such display is thus seriously degraded.
To resolve the electron-beam diffusion problem of the conventional bipolar or tri-polar field-emission display, tetra-polar (as shown in FIG. 3) or penta-polar field-emission display has been proposed. The tetra- or penta-polar field-emission display has a converging electrode layer in addition to the basic components of the bi- or tri-polar field-emission display. Therefore, the electron emission generated from the cathode can be focused or converged into a concentrated beam to precisely and sufficiently impinge the phosphor of the corresponding anode unit. Thereby, gamut is prevented to appear in the image.
The converging electrode layer formed between the cathode structure and the anode structure of a tetra-polar field-emission display provides a voltage to converge the electron beam. The fabrication process of this type of tetra-polar field-emission display includes forming a converging electrode layer on a gate electrode layer by photolithography, or forming a shadow mask between the cathode and anode structures to serve as the converging electrode layer. Either type of converging electrode layer does not only increase the complexity of fabrication, but also increase the material cost.